1. Field of the Invention
The invention relates to inductor devices, and in particular to high frequency integrated inductor devices with high quality factor.
2. Description of the Related Art
Both passive and active electronic devices in electronic circuits have been developed towards technique regimes such as high frequency, broad band, and miniaturization, and are applicable to a variety of electronic and communication devices including telecommunication, digital computer, portable and household appliance. The embedization of passive and active electronic devices has become one of the main developing trends to shrink electronic circuit area. More particularly, embedded passive devices such as embedded inductors have been replacing conventional surface mounted technique (SMT) passive devices.
Relatively more fabrication steps and materials however, are needed for embedding of passive devices into a substrate. In addition, some parasitic effects are generated due to embedding of inductor devices, reducing electrical performance. For example, when conventional inductor devices are embedded into a substrate, both inductance and quality factor of the inductor device are reduced due to substrate loss. Thus, embedded inductor devices with higher inductance and quality factor are needed to meet the requirements of a state of the art electronic circuit. Conventionally, the three characteristics of importance for an inductor device comprise inductance, quality factor and self-resonance frequency (SRF).
Conventional embedded inductor devices are limited by the substrate and have greater parasitic capacitor effect affecting quality factor and SRF. Specifically, a conventional solenoid inductor winds through the substrate generating parasitic capacitor effect, thus limiting applications to lower quality factor applications. Moreover, parasitic capacitor effect can further reduce SRF, limiting the frequency and other potential applications.
Conventional solenoid inductor devices comprise conductive coils with constant length and width, thereby generating parasitic capacitor effect. Inductance, quality factor and SRF of the constant solenoid inductor device are degraded due to parasitic capacitor effect. Therefore, a gradually sized solenoid inductor device is needed to constrain parasitic capacitor effect, thus broadening SRF range and enhancing inductance and quality factor of the inductor device.
Referring to FIG. 1, a schematic view of a conventional solenoid inductor device, a solenoid inductor device 10 comprises a solenoid coil 20 spirally winding a tetragonal core 15. The tetragonal core 15 comprises air or magnetic materials. The inductance of an ideal solenoid inductor device can be calculated by the following equation:
  L  =      μ    ⁢                  ⁢                            N          2                ⁢        Ac            lc      
where L denotes the inductance of the ideal solenoid inductor device, N denotes the number of winds of the solenoid coil, Ac denotes the area of the solenoid coil, and lc denotes the length of the solenoid coil. The inductance of the ideal solenoid inductor device is proportional to the product of the square of the number of winds N by area of the solenoid coil.
A conventional embedded solenoid inductor device is different from the ideal solenoid inductor device in that coupling occurs between the substrate and the solenoid coil, and between adjacent windings of the solenoid coil, thereby generating parasitic capacitor effect. As the applied frequency is increased, the parasitic capacitor effect becomes more prevalent and reducing SRF.
U.S. Pat. No. 6,509,821, the entirety of which is hereby incorporated by reference discloses an inductor device comprising a coil with tapered windings. Metal wires may be used for gradual winding. However, the conventional gradually winded inductor device is difficult to integrate into a substrate structure. The width of the winding must remain constant, thereby placing a constraint on the quality factor of the inductor device.
Referring to FIG. 2, a schematic view of a conventional embedded solenoid inductor device, a conventional embedded solenoid inductor device 30 comprises a substrate 31 and a conductive coil 40 with a plurality of windings surrounded and disposed on the substrate 31. A winding comprises a first conductive segment 33 disposed on a first surface of the substrate 31. A second conductive segment 32 is disposed on a second surface of the substrate 31. A first conductive via hole 34 perforating the substrate 31 connects the first conductive segment 33 and the second conductive segment 35. A second conductive via hole 36 perforating the substrate 31 connects the second conductive segment 35 to a first conductive segment of the following winding. The conventional embedded solenoid inductor device 30 comprises uniform length and width windings. Specifically, both the length and width of all the first conductive segments are equal throughout windings. The conductive coil 40 further comprises an input end 32 and an output end 37. The input end 32 is connected to the first conductive segment 33 at the start of the windings. The output end 37 is connected to the second conductive segment at the end of the winding.
A need exists for an embedded solenoid inductor device for high frequency application which constrains parasitic capacitor effect, thus broadening application frequency range while enhancing inductance and quality factor.